Study designs with data-dependent sample sizes provide an attractive alternative to fixed sample size designs because interim decisions may reduce cost and decrease the duration of the study. Two groups of such sequential procedures, namely, groups sequential designs (GSD) and sample size re-estimation (SSR) procedures, are popular examples of studies with random sample sizes [see [1]}, [2]}, [3]}, [4]}]. Our manuscript mostly deals with GSDs and SSR, but other adaptive designs may also benefit from the theoretical findings reported here.
